A: The universal definition of geothermal is "pertaining to the heat of the earth." Indeed, the earth's heat has been used for millennia: the Romans used underground hot water and steam to heat buildings and spas.

Today, new technologies such as geothermal heat pump systems are used to tap the stored energy beneath the earth's surface.

While ambient air temperatures fluctuate from season to season, underground temperatures do not. In fact, about four to six feet below the surface, the temperature of the earth remains the same all year, around 55 degrees. A geothermal heat pump system, consisting of an indoor unit and a ground loop, utilizes these constant temperatures to heat and cool the house as well as heat water. The "loop" is basically a pipe filled with a re-usable water-based solution and buried four to five feet deep that "loops" for 100 to 400 feet, depending on the size of the house it will serve.

In the winter, when the air temperature is in the 30s or below, water circulating through the ground loop absorbs the 55-degree heat underground and carries it to the house. The indoor unit then compresses the heat to a higher temperature and distributes it through the rooms. In the summer when temperatures are in the 80s or 90s, this process is reversed: water circulating through the loop absorbs the heat from the house and carries it underground, where it is dispersed by the cooler 55-degree temperature.

Although costly to install, geothermal systems can save up to 60 percent on monthly energy bills, and thus can more than pay for themselves over time. For example, I've had a geothermal system for 14 years, and my monthly utilities on a 2300-square-foot house are around $100 per month. Of course, my house is also well insulated, but the geothermal system has definitely helped to reduce costs.

Horizontal ground loops are used when there's enough land to run up to 400 feet of underground pipe away from the house, while vertical loops– which can be 75 to 300 feet deep– are used when land space is limited. In one case, we were able to run loops into a client's dry well, and in another case we ran loops along a thin strip of land along a client's driveway because that was the only space available.

But geothermal energy can also be produced without digging. If there is surface water on the property, loops running on the bottom of lakes or ponds can produce the same geothermal effect. In addition, open loop systems can pull water directly from ponds or lakes or from an underground well to heat and cool a house.

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2 comments

River Rat January 11th, 2008 | 10:10pm

Do these geo thermal things work to cool beer when you are tubing down the James?

Dan1101 January 14th, 2008 | 3:10pm

Only if you want to dig a hole and stay anchored at one place in the river. :P